Texture, Material problem when exporting to three.js
Set the diffuse color to full white. 

Blender internal materials do not overlay the diffuse color over the texture (blending) while depending on your application / three.js shaders probably do take diffuse color into account as a color overlay.

Als make sure to set the intensity to 1 as that might change the RGB values upon export. Blender default materials have a gray value and intensity 0.8 as default, so you could write a little script to update all the materials:

import bpy

for material in bpy.data.materials:
    material.diffuse_color = (1.0, 1.0, 1.0)
    material.diffuse_intensity = 1
    material.specular_intensity = 1


A neutral white should therefore produce the proper result.